Secondary IgE Responses Research Articles

Memory Generation and Re-Activation in Food Allergy.

Recent evidence has highlighted the critical role of memory cells in maintaining lifelong food allergies, thereby identifying these cells as therapeutic targets. IgG+ memory B cells replenish pools of IgE-secreting cells upon allergen exposure, which contract thereafter due to the short lifespan of tightly regulated IgE-expressing cells. Advances in the detection and highly dimensional analysis of allergen-specific B and T cells from allergic patients have provided insight on their phenotype and function. The newly identified Th2A and Tfh13 populations represent a leap in our understanding of allergen-specific T cell phenotypes, although how these populations contribute to IgE memory responses remains poorly understood. Within, we discuss the mechanisms by which memory B and T cells are activated, integrating knowledge from human systems and fundamental research. We then focus on memory reactivation, specifically, on the pathways of secondary IgE responses. Throughout, we identify areas of future research which will help identify immunotargets for a transformative therapy for food allergy.

A B Cell Epitope Peptide Derived from the Major Grass Pollen Allergen Phl p 1 Boosts Allergen-Specific Secondary Antibody Responses without Allergen-Specific T Cell Help.

More than 40% of allergic patients suffer from grass pollen allergy. Phl p 1, the major timothy grass pollen allergen, belongs to the cross-reactive group 1 grass pollen allergens that are thought to initiate allergic sensitization to grass pollen. Repeated allergen encounter boosts allergen-specific IgE production and enhances clinical sensitivity in patients. To investigate immunological mechanisms underlying the boosting of allergen-specific secondary IgE Ab responses and the allergen epitopes involved, a murine model for Phl p 1 was established. A B cell epitope–derived peptide of Phl p 1 devoid of allergen-specific T cell epitopes, as recognized by BALB/c mice, was fused to an allergen-unrelated carrier in the form of a recombinant fusion protein and used for sensitization. This fusion protein allowed the induction of allergen-specific IgE Ab responses without allergen-specific T cell help. Allergen-specific Ab responses were subsequently boosted with molecules containing the B cell epitope–derived peptide without carrier or linked to other allergen-unrelated carriers. Oligomeric peptide bound to a carrier different from that which had been used for sensitization boosted allergen-specific secondary IgE responses without a detectable allergen-specific T cell response. Our results indicate that allergen-specific secondary IgE Ab responses can be boosted by repetitive B cell epitopes without allergen-specific T cell help by cross-linking of the B cell epitope receptor. This finding has important implications for the design of new allergy vaccines.

Can persistent IgE responses be suppressed?

Since the discovery ofIgE in the late 1960s (Ishizaka, Ishizaka & Hornbrook, 1966; Johansson & Bennich, 1967) several animal models have been developed to study the regulation of IgE. IgE responses in atopic people are typically long lived and can be maintained when they are no longer exposed to allergen as in hay fever patients outside the pollen season. Such responses have proved difficult to produce in most species, with the exception of mice, and after an initial burst of IgE when first immunized, the response generated is rapidly suppressed. The artificial induction of IgE responses in rodents has required the use of adjuvants such as aluminium hydroxide and Bordatella pertussis or concomitant nematode infection (Jarrett & Stewart, 1972). T cells play a central role in regulating IgE responses (Okumura & Tada, 197 la; Katona, Urban & Finkelman, 1988), and as well as providing help for IgE B cells, they are capable of suppressing both primary and secondary IgE responses (Okumura & Tada, 1971b; Holt, Batty & Turner, 1981a). Thus two opposing functions for T cells in IgE regulation can be seen. These effects are mediated at least in part by T cell-derived cytokines. High levels of interleukin-4 (IL-4) were found to potentiate IgE synthesis from lipopolysaccharide (LPS) stimulated murine B cells in vitro (Coffman & Carty, 1986) and this effect could be antagonized with interferon-gamma (IFN-y) (Snapper & Paul, 1987). Anti-IL-4 antibody (Finkelman et al., 1986, 1988a) or IFN-y (Finkelman et al., 1988b) both suppress antigen and Nippostrongylus braziliensis-induced IgE responses in vivo. With N. braziliensis infestation, IgE levels spontaneously decline following worm expulsion but similar effects were also seen with anti-IL-4 and IFN-y in Heligmosomoides polygyrusinfested mice, where the worm is not expelled and IgE levels do not fall (Finkelman et al., 1990). The secondary IgE response produced with antigen and Al(OH)3 was largely but not completely inhibited with anti-IL-4 (Finkelman et al., 1990); these investigators conclude that the role of IL-4 in the maintenance of an IgE response is to recruit

Isotype-selective abrogation of established IgE responses

Chemically modified allergens have been extensively studied in an attempt to develop materials of increased efficacy and improved safety for use in the immunotherapy of allergic disease. Most of the strategies that have been developed yield products that strongly inhibit de novo IgE responses but have only marginal impact on ongoing IgE responses. We report the virtual abrogation of pre-established murine anti-ovalbumin IgE responses using a glutaraldehyde-polymerized ovalbumin preparation (OA-POL) of Mr 3.5 x 10(7). Secondary IgE responses are inhibited by 97-99% over a period of at least 8 months following three i.p. courses of OA-POL treatment. Administration of five additional ovalbumin [Al(OH)3] booster immunizations over this period fails to alter this unresponsive state. The inhibition of antigen-specific IgE responses is isotype specific.

Inhibition of Eosinophil Infiltration into the Mouse Peritoneal Cavity by a Traditional Chinese Medicine, Bu-Zhong-Yi-Qi-Tang (Japanese Name: Hochu-Ekki-To)

Our previous study showed that the serum level of antigen-specific IgE antibodies in primary response was decreased by a traditional Chinese medicine, Bu-zhong-yi-qi-tang (Japanese name; Hochu-ekki-to, HOT). In this study, we examined inhibition of secondary IgE response and of eosinophil infiltration by HOT. BALB/c mice were intraperitoneally immunized with aluminum hydroxide adsorbed with DNP-KLH (DNP-KLH + alum) on day -14 and on day 0. In mice treated with HOT daily from day -14, the serum level of antigen-specific IgE antibodies after the secondary immunization was significantly decreased compared to that in mice not treated with HOT. Eosinophils increased in number after 6 and 24 hr, and CD4+ T cells in the peritoneal cavity increased in number 24 hr after the secondary immunization. HOT suppressed accumulation of eosinophils and CD4+ T cells in the peritoneal cavity. Furthermore, HOT suppressed the numbers of IL-4- and IL-5-producing cells 24 hr after the secondary immunization, but did not inhibit the number of IFN-gamma-producing cells. HOT also suppressed IL-5 mRNA expression. Furthermore, HOT also inhibited antigen-induced late-phase reaction (LPR) in the skin. These results suggested that HOT exhibited anti-allergic effects mainly by inhibiting Th2 cell responses.

Seasonal Rise in Interleukin-4 during Pollen Season is Related to Seasonal Rise in Specific IgE for Pollens but not for Mites

Since IL-4 plays a key role in inducing and increasing the generation of not only primary polyclonal but also secondary specific IgE responses by B lymphocytes, a seasonal increase in IL-4 is likely to be involved in such seasonal rises in specific IgE in seasonal allergic rhinitis. The first aim of this study was to investigate the possible seasonal increase in serum IL-4 in patients with seasonal allergic rhinitis due to Japanese cedar pollens. If serum IL-4 increases in response to seasonal pollen exposure and is responsible for the seasonal increase in pollen-specific IgE in sera, this increase in IL-4 might theoretically affect specific IgE synthesis for other allergens. The second aim was to investigate the effect of natural pollen exposure on serum concentrations of house dust mite-specific IgE in patients who have seasonal allergic rhinitis and concurrent perennial allergic rhinitis due to house dust mites. This study included 55 adult patients with seasonal and perennial allergic rhinitis due to Japanese cedar pollens and Dermatophagoides farinae (D. farinae). Venous blood was collected twice from each patient, before and during the cedar pollen season 1996, to determine IL-4, cedar pollen-specific IgE and D. farinae-specific IgE in sera. Both IL-4 and pollen-specific IgE in sera were significantly increased during the pollen season, and the seasonal increase rate in pollen-specific IgE was significantly correlated with the seasonal increase rate in IL-4. By contrast, D. farinae-specific IgE was not changed during the pollen season in these patients. In conclusion, an elevation of IL-4 in sera during the pollen season may play an important part in the seasonal rise in pollen-specfic IgE, and enhancement of specific IgE synthesis is likely to need not only an increase in IL-4 but also an increase in the number and/or capacity of specific IgE-secreting B cells.

Nasal provocation with allergen induces a secondary serum IgE antibody response

The study of the IgE response to seasonal antigen exposure is limited by its occurrence once a year and by the variability of patient exposure to pollens. To overcome these problems, we investigated whether nasal challenge with antigen causes an increase in serum anti-ragweed IgE levels. We challenged individuals with ragweed allergy intranasally with nanogram quantities of ragweed antigen extract and measured their serum anti-ragweed IgE levels before and at weekly intervals after challenge. In a series of studies we found that there was a reproducible rise in antigen-specific serum IgE levels beginning the first week after challenge that plateaued at about 180% of baseline levels during the fourth week and remained elevated for 8 weeks. Not all individuals showed this response. The magnitude of the allergen-specific IgE response to nasal challenge appeared to be greater than the response to seasonal exposure. Treatment with intranasal beclomethasone before challenge did not affect the response. The results demonstrate a human in vivo model for the study of the antigen-specific secondary IgE response to allergen. (J Allergy Clin Immunol 1997;100:505-10.)

Inhibition of primary and recall allergen-specific T helper cell type 2-mediated responses by a T helper cell type 1 stimulus.

Allergic responses are characterized by the production of Ag-specific IgE Abs that are dependent upon Th2-mediated T cell help. We determined whether heat-killed Brucella abortus (BA), an inducer of Th1 responses, could influence the allergic Th2-mediated IgE response to OVA adsorbed to alum (O/A). BA plus O/A, but not O/A alone, induced high levels of mRNA for IFN-gamma and IL-12 promptly after injection. Furthermore, initial treatment with BA plus O/A rendered both BALB/c and C57Bl/6 mice incapable of mounting high IgE responses even after repeated challenges with allergen alone. Long term abrogation of anti-OVA IgE correlated with an increased frequency of IFN-gamma-secreting OVA-specific cells and a decreased frequency of IL-4-secreting OVA-specific cells. Initial treatment with anti-IL-12 prevented BA-induced early IFN-gamma production and secondary IgG2a responses, but did not abrogate IgE suppression. Additionally, secondary OVA-specific IgE responses were down-regulated by BA conjugated to OVA or by BA given with O/A. BA-induced down-regulation of secondary IgE responses was associated with increased frequency of Ag-specific IFN-gamma-secreting cells. These results suggest the possibility that even recall Th2-mediated immune responses can be attenuated if Ag is given with a carrier or adjuvant that induces potent Th1-promoting cytokines.

Relative immunogenicity of ß-lactoglobulin, bovine serum albumin, and a model acid whey product

The relative immunogenicities of bovine ß-lactoglobulin (ß-LG) and bovine serum albumin (BSA) were investigated using a rat model system. ELISAs were developed to quantify antibody titers in Sprague-Dawley rats injected intraperitoneally with dosages of ß-LG ranging from 0.01 to 1000 μg, and dosages of BSA ranging from 0.1 to 1000 μg. Primary IgG and IgE responses to BSA increased with increasing dosage of BSA, with a minimum of 100 and 1000 μg (respectively) necessary for responses significantly (P < 0.05) greater than that of untreated controls. Secondary (boosted) IgE responses to BSA were not significantly (P < 0.05) greater than primary responses. Greater specific IgG and IgE responses to ß-LG occurred at 3 than 2 weeks post-injection, and at lower dosages (0.1 or 1.0 μg). Compared over a range of dosages, the immunogenicities of BSA and ß-LG did not differ significantly (P > 0.05). The results of this study may aid in developing operating parameters for affinity absorption methods that selectively remove allergenic proteins from milk or acid whey.

The development of IgE+ memory B cells following primary IgE immune responses.

We studied whether long-lived IgE+ memory B cells develop following three types of primary IgE immune responses. Immunization of mice with anti-IgD antibody induced a T cell-dependent, interleukin (IL)-4-dependent primary IgE response and the formation of IgE isotype switched (IgE+) memory B cells. These IgE+ memory B cells could be stimulated in vivo by injection with goat anti-IgE antibodies to produce a profound IL-4-independent memory IgE response. By contrast, both infection of mice with Nippostrongylus brasiliensis or repeated immunization with benzylpenicilloyl-keyhole limpet hemocyanin (BPO-KLH) in alum stimulated good primary IgE responses and profound memory T cell-dependent antigen-specific IgE responses, but failed to induce the development of long lived IgE+ memory B cells because they could not be recalled with goat anti-IgE antibodies. Mice receiving double immunizations combining anti-IgD with either N. brasiliensis infection or BPO-KLH immunization mounted significant goat anti-IgE-induced secondary IgE responses, but no N. brasiliensis or BPO-KLH-specific IgE could be detected. This indicates that the N. brasiliensis and BPO-KLH induced immune responses do not suppress the development of IgE+ B cells, but rather, do not provide the necessary conditions for their formation. Taken together these data indicate that long-lived IgE+ B cells fail to develop during the primary IgE response to N. brasiliensis infection or BPO-KLH immunization. By contrast, significant numbers of IgE+ memory B cells form during the primary IgE immune response induced by anti-IgD immunization. Our observations suggest that immunization protocols involving membrane IgD cross-linking and limited duration of cognate T cell help are necessary for the formation of IgE+ memory B cells. It will be important to determine the relevance of membrane IgD interaction with allergens, as this would influence the design of new therapies for the treatment of allergy and asthma.

Nebulized IFN-gamma inhibits the development of secondary allergic responses in mice.

The effects of nebulized IFN-gamma on primary and secondary IgE production and development of airway hyper-responsiveness (AHR) were investigated. BALB/c mice received primary exposure to aerosolized OVA daily for 10 days and developed anti-OVA IgE responses, immediate cutaneous reactivity to OVA, and altered airway function when assayed on day 12. After secondary exposure to OVA challenges on days 30 and 31, these mice developed an amplified IgE response, heightened cutaneous reactivity to OVA and AHR when measured on day 37. Administration of IFN-gamma for 13 days, beginning 3 days prior to and during primary OVA sensitization, resulted in a decrease in anti-OVA IgE, increases in serum anti-OVA IgG2a levels, a decrease in cutaneous reactivity to OVA, and normal airway function when assessed on day 12 after primary sensitization. This treatment also prevented the development of secondary anti-OVA IgE responses and altered airway responsiveness but did not induce a secondary rise in anti-OVA IgG2a in the serum measured on day 37. Treatment with IFN-gamma on days 26 to 30, well after primary responses were established but just prior to secondary OVA challenge, abolished the development of secondary anti-OVA IgE responses, resulted in an increase in anti-OVA IgG2a in the serum, and prevented the development of AHR. In vitro, CD4+ T cells obtained from OVA-sensitized mice treated with either "early" or "late" IFN-gamma inhibited IgE production. Delivery of IFN-gamma to the airways can prevent secondary allergen sensitization even after primary sensitization has been achieved and this effect is mediated by CD4+ T cells.

Secondary IgE Responses In Vivo are Predominantly Generated Via γ1ɛ‐Double Positive B Cells

We have recently developed a model in which mice were treated with IL-4 after primary immunization, resulting in elevated total serum IgG1 and IgE levels, but decreased antigen-specific levels and memory formation for these isotypes. In this report, we describe that these effects of IL-4 are mediated at the B cell and not the T-cell level. Major changes occurred in the gamma 1 epsilon-double positive B-cell population which is increased as a result of IL-4 treatment. Moreover, it is shown that gamma 1 epsilon-double positive B cells can develop in vitro out of gamma 1-positive primed B cells and that these double positive cells can differentiate into IgG1- and IgE-secreting cells. The existence of gamma 1 epsilon-double positive memory B cells can explain the differences in cytokine dependence of TNP-specific memory IgG1 and IgE responses found after adoptively transferring primed spleen cells into irradiated naive recipients. Whereas the IL-4 independent TNP-specific memory IgG1 responses could be blocked efficiently by neutralizing IL-5 and IL-6, TNP-specific memory IgE responses were virtually not susceptible to such treatment. These IgE responses were also not susceptible to IFN-gamma, used in doses that could inhibit the primary IgE response. Inhibition of the TNP-specific memory IgG1 response by neutralizing IL-5 and IL-6 is accompanied by a 10-fold increase of the IL-4 independent TNP-specific IgE memory response. These data indicate that secondary IgE responses primarily result from B cells that are either switched to IgG1, or are double positive for IgG1 and IgE, thereby suggesting a minor role for epsilon-single positive B cells in secondary IgE responses.

Prolonged In Vivo IL‐4 Treatment Inhibits Antigen‐Specific IgG1 and IgE Formation

IL-4 is obligatory for primary IgE responses, whereas primary IgG1 and secondary IgE responses are partially IL-4 independent. To investigate the effect of IL-4 on the antigen-specific memory formation for these isotypes, BALB/c mice were treated after primary TNP-KLH immunization with recombinant IL-4 for a period fo 4 months. This prolonged presence of a high IL-4 level resulted in increased serum levels of total IgG1 and IgE, whereas total IgG2a did not change. The expression of CD23, but not I-Ad, increased on the splenic B cells. IL-4 treatment did not affect the IL-4 production by Con A stimulated spleen cells, whereas it did decrease the IFN-gamma production. In the same mice the TNP-specific IgG1 and IgE serum levels, however, were decreased. Similar results were found when the antigen was continuously present during the IL-4 treatment. Furthermore, it was shown that IL-4 decreased the formation of IgG1 and IgE memory cells. These results point to different effects of IL-4 in regulating antigen-specific and bystander responses.

Effects of syngeneic anti-IgE antibodies on the development of IgE memory and on the secondary IgE response.

The prolonged inhibition of IgE synthesis in mice caused by perinatal inoculation of IgE is attributable, at least in part, to the formation of anti-IgE antibodies. The induction of unresponsiveness with respect to IgE synthesis requires that IgE be administered during a brief interval (2 to approximately 10) days after birth, that corresponds with the time period during which anti-IgE antibodies are induced. Passive administration of syngeneic anti-IgE also inhibits IgE synthesis. We have now investigated the effect of anti-IgE on the induction of memory for IgE production and on secondary IgE responses. Syngeneic anti-IgE antibodies were found to inhibit secondary IgE responses directly during immunization or after adoptive transfer of primed cells. Anti-IgE did not, however, prevent the induction of memory cells for IgE synthesis or cause the loss of memory for IgE synthesis. Inhibition of a secondary IgE response was found to require the presence of anti-IgE and was lost when anti-IgE antibodies were cleared from the mouse. After the transfer of primed cells and secondary challenge anti-IgE was inhibitory only when given during the first 3 to 5 days, after which the primed cells became resistant to inhibition. The failure of anti-IgE to prevent the induction of IgE memory cells is discussed in terms of class switches that occur during the transition from IgM to IgE production.

The Secondary Antigen-Specific IgE Response in Murine Lymphocytes Is Resistant to Blockade by Anti-IL4 Antibody and an Antisense Oligodeoxynucleotide for IL4 mRNA

In order to investigate the role of interleukin 4 (IL4) in the induction of antigen-specific IgE responses, we established culture conditions which allow the induction of anti-trinitrophenyl(TNP) IgE response by the coculture of TNP-keyhole limpet hemocyanin-primed C3H B cells with conalbumin (CA)-specific type 2 helper T (Th2) cell clone, D10.G4.1 in the presence of TNPCA. A maximum level of anti-TNP IgE was secreted at 1 μg/ml TNP-CA. By using filter-separated double-chamber culture plates, the physical contact between T cells and B cells was shown to be necessary in this response. Anti-TNP IgE synthesis was not significantly suppressed in the presence of 20-40 μg/ml monoclonal anti-IL4 (11B11), nor was the response further enhanced by the addition of recombinant IL4. 11B11 added together with anti-IL5 had also no suppressive effects on the IgE response. This apparent independence on IL4 might be due to the fact that IL4 is transferred from T cells to B cells in a transsynaptical way that would be refractory to the neutralization by 11B11. in order to test this possibility, we synthesized the phosphorothioate analogue of an antisense oligodeoxynucleotide against IL4 mRNA (S-oligo) for inhibiting IL4 production from Th2 cells specifically. S-oligo was effective at 10-20 μg/ml in suppressing IL4 production from D10.G4.1 cells by 80-90%. It was demonstrated that S-oligo, either alone or in combination with 11B11, did not significantly suppress anti-TNP IgE response. These results suggest that antigen-specific IgE response in primed B cells does not depend on IL4, but requires cognate interaction with Th2 cells.

Suppression of IgE antibody response in mice by a naphthalene derivative, TEI-6472

In the present report, we investigated suppressive effects of a naphthalene derivative, (7E)- N-(2-carboxyphenyl)-8-(2-naphthyl)-5,6-trans-5, 6-methano-7-octenamide L-lysine salt (TEI-6472), on in vitro and in vivo antigen-specific IgE response. Anti-trinitrophenyl (TNP) IgE response induced in vitro in TNP-keyhole limpet hemocyanin (KLH)-primed murine spleen cells was suppressed by about 60% in the presence of 10 −6 M TEI-6472. On the other hand, anti-TNP IgG1 and IgM response were not significantly suppressed under the same conditions. Proliferative responses of BALB/c spleen cells stimulated by lipopolysaccharide, concanavalin A or allogeneic spleen cells were not inhibited by TEI-6472 at 10 −6-10 −5 M. Interleukin 4 production from helper T-cell clone, D10.G4.1 was suppressed only slightly (less than 20%) at 10 −6 M TEI-6472. This compound was also effective in suppressing secondary anti-TNP IgE response in mice that were immunized twice with TNP-KLH and alum. When 10–20 mg/kg/day TEI-6472 was administered s.c. for 5 consecutive days starting from one day before the first and the second immunization, secondary anti-TNP IgE response was inhibited most strongly (40–45%). Anti-TNP IgG1 response was also inhibited but to a smaller extent (20–24%), while anti-TNP IgM response was suppressed only slightly (0–15%). These results suggest that, under appropriate conditions, TEI-6472 can suppress IgE responses more preferentially both in vitro and in vivo.

Regulation of IgE production in pre-sensitized animals: in vivo elimination of alveolar macrophages preferentially increases IgE responses to inhaled allergen.

Intratracheal inoculation of dichloromethylene diphosphonate encapsulated in liposomes leads to the rapid accumulation of this drug in alveolar macrophage (AM) phagolysosomes, and the death of the majority of these cells over the ensuing 24-48 hr. The technique is highly selective for phagocytes and has no detectable side-effects on other cells in the lung. The present experiments demonstrate that following AM depletion, pre-sensitized animals respond to aerosol challenge via secondary serum IgE (but not IgG) responses, and the accumulation of large numbers of allergen-specific and non-specific antibody forming cells in respiratory tract regional lymph nodes and in lung and airway tissues; the latter comprise both IgE and IgG plasma cells, which were detected in the approximate ratio of 2.5:1. Moreover, aerosol challenged AM-depleted animals develop large mononuclear cell infiltrates in the lung and airways, which includes a substantial CD4+ T-cell component. These results suggest a major role for AM in regulating the magnitude of secondary IgE responses to inhaled allergen.

Antigen concentration determines helper T cell subset participation in IgE antibody responses

A recently developed in vitro system for antigen-stimulated primary and secondary murine IgE antibody responses has been used to define (a) the relative participation of the Th1 and Th2 cell-derived lymphokines IFN-γ and IL-4, respectively, in such responses, and (b) the role of antigen concentration in determining functional helper T cell activity. These studies confirm that IL-4 and IFN-γ exert regulatory effects on IgE synthesis, but the nature and extent of their respective effects on primary and secondary IgE responses differ. Thus, primary IgE responses are considerably more sensitive to and dependent on IL-4 than are secondary IgE responses since (1) anti-IL-4 monoclonal antibody totally inhibited primary IgE responses, but only partially affected secondary responses; and (2) exogenously added IL-4 could stimulate primary IgE responses to optimal antigen concentrations, but had no effect on secondary IgE production. Likewise, antigen-stimulated primary IgE responses are about eightfold more sensitive than are secondary responses to the inhibitory effects of IFN-γ. Studying the effect of antigen dose on the quantity of IgE antibody produced revealed that although IFN-γ could be detected by ELISA in cultures exhibiting high-dose antigen-dependent diminution of IgE production, anti-IFN-γ monoclonal antibody could not reverse this phenomenon. Thus, IFN-γ is not soley responsible for decreased IgE synthesis associated with high-dose antigen exposure. IL-4 activity was detected in the fluid from cultures stimulated with low, but not high, levels of antigen. Moreover, addition of exogenous IL-4 restored IgE production to normal levels in cultures exposed to high antigen concentrations. Therefore, it appears that high levels of antigen result in selective stimulation of Th1 cells which produce IFN-γ, and diminished activation of IL-4-producing Th2 cells. These results help explain observations regarding the influence of antigen dose on the generation of experimental and clinical IgE antibody responses in vivo.

B cell activator. Effects on B cell expression of CD23, proliferation, and antibody secretion.

The studies herein describe a B cell hybridoma-derived, low m.w. (less than 1000 Da), hydrophilic mediator denoted B cell activator (BCA). BCA stimulates B cell expression of IgE-specific FcR (Fc epsilon RII or CD23) in a manner similar to IL-4. However, BCA can be readily distinguished from IL-4 because it does not 1) enhance B cell Ia expression; 2) bind 11B11 anti-IL-4 mAb; or 3) elicit superinduction of Fc epsilon RII expression or IgE production in cultures of LPS-activated B cells. Moreover, BCA is considerably more mitogenic than IL-4 for LPS-activated B cells and, in contrast to IL-4, lacks mitogenicity for anti-mu-activated B cells. BCA can enhance IgG2b and IgG3 production by LPS-activated B cells, responses that are suppressed by IL-4. BCA alone did not stimulate IgE and IgG1 production by LPS-activated B cells, but exerted synergistic activity when combined with IL-4 in stimulating secretion of these antibody isotypes. Finally, secondary Ag-driven IgG1, IgE, and IgA antibody responses can be stimulated by BCA in vitro. Thus, BCA appears to be a novel mediator with broad B cell activation properties.

Efficacy of liposome entrapped allergen in down regulation of IgE response in mice.

The effect of liposome entrapped allergen on primary, secondary and ongoing IgE response was studied in mice. It was observed that mice primed with liposome entrapped allergen maintained significantly lower levels of serum specific IgE as compared to that of controls primed with allergen. Although alum adsorbed allergen could induce IgE synthesis in mice primed with liposome entrapped allergen the increase in serum specific IgE levels was lower than the animals primed and challenged with alum adsorbed allergen. On the contrary when BALB/c mice were primed with alum adsorbed allergen to induce IgE synthesis subsequent challenge by liposome entrapped allergen could down regulate the serum specific IgE response. Serum specific IgG response did not show any significant difference between the two groups. There was an increase in T suppressor cell subpopulation as measured by immunofluorescence technique in mice injected liposome entrapped allergen as compared to that in controls. The results indicate that liposome entrapped allergens may prove to be safe and effective in immunotherapy by reducing the allergenic response of the allergen at the same time increasing the antigenicity.